Medical devices are used to treat human or animal tissue in many ways. Many such devices are elongated with one end adapted to be held, either by hand or by a robotic or other mounting, with the other end being comprised of a parent metal and adapted to contact or otherwise interact with human or animal tissue.
By way of an example, a needle has a proximal end adapted to be mounted to a syringe cannula for injection or withdrawal of fluids from a body, or to a length of flexible tubing such as in an IV catheter. In either case, the metal distal end is adapted to be inserted into and through human or animal skin and blood vessels for passage of fluids therethrough.
One specialized type of medical instrument is an electrosurgical knife or RF scalpel which is used to cut or cauterize tissue. Typical of such instruments is that they use an elongated medical device referred to as an “active electrode,” or tip, sometimes also referred to as a “Bovie” tip, to contact and cauterize the tissue.
In electrosurgery, an electric current is used to cut or cauterize human or animal tissue. Currently, there are two main types of electrosurgical apparatus in use. Depending on the number of electrodes used in the cutting and cauterization, these instruments are referred to as, unipolar or bipolar. The tip is electrically conductive and cooperates with another conductor, such as a dispersive electrode (monopolar or unipolar) or an adjacent electrode or tip (bipolar), to allow current flow at the site to be treated. These tips have a proximal end adapted to be mounted to the knife, with the distal end defining an active metal electrode area to cut or cauterize tissue of interest.
In a unipolar electrosurgical apparatus, current (usually “RF” current) is supplied to an electrode which is used to cut or cauterize tissue. When in use, current flows through the electrode to the patient and the circuit is completed using a “patient plate” on which the patient lies. The surface area of the electrode through which current flows (the “active electrode area” or “active electrode surface”) is small relative to the area of the patient plate and therefore an intense local current density is generated at the electrode. This results in cutting or cauterization of the tissue in the immediate proximity of the electrode. An example of a unipolar electrosurgical instrument is described in U.S. Pat. No. 4,927,420.
In a bipolar electrosurgical apparatus, the “patient plate” of the unipolar apparatus is replaced by a second electrode separated from the first electrode by a small gap. In operation, an intense local current density is generated between the electrodes and results in cutting or cauterization of the tissue between the electrodes. Examples of bipolar electrosurgical instruments are described in U.S. Pat. Nos. 5,396,900, 5,217,458, 5,342,381, and 5,395,369.
The electrodes used in both unipolar and bipolar apparatus come in a wide variety of shapes, sizes, and configurations. Depending on the surgical requirements, the electrodes can be in any of a variety of shapes, non-limiting examples include needles, loops, spatulas, scalpel blades, scissors, forceps, and balls. Electrosurgical techniques have also been extensively used for endoscopic surgery. Since electrosurgical tools can be made much smaller than their conventional counterparts, electrosurgery is especially suited to this type of surgery. A wide variety of shapes and configurations of endoscopic electrodes have been described as seen in the herein cited U.S. Pat. Nos. 5,396,900, 5,217,458, and 5,395,369.
In conventional electrosurgical instruments, the active electrode surfaces are usually made of stainless steel. However, there is a well known drawback to using stainless steel electrodes; namely, that burnt tissue layers adhere to the electrode surface during the electrosurgical procedure. This drawback is especially disadvantageous during endoscopic surgery as the cleaning of the electrosurgical tip is an arduous task, adding considerable time and expense to each procedure.
It is thought that the mechanism that causes tissue to stick to the instruments is as follows. During electrosurgical procedures, an intense electric current density is generated between the electrodes and the tissue. In fact, the electrosurgical procedure often causes arcing between the electrode and the tissue. The high current density causes intense heating which carburizes the tissue and results in the required cutting or cauterization. The electrodes of the conventional instruments react with this carburizing atmosphere and this forms adherent burnt tissue layers on the surface of the electrodes. During the electrosurgical procedure, burnt tissue begins to build up on the instrument surfaces in the form of a black film. When this build-up thickens and thus reduces the current density between the electrode and the tissue, the tissue begins to stick to the hot black film. The surgeon is then forced to stop the operation and clean the electrosurgical instrument. This cleaning, in addition to being time consuming, can require enough force to scratch the surface of the stainless steel. These scratches roughen the surfaces of the instrument and this in turn causes tissue residue to build up faster and results in more sticking.
The metal electrodes of electrosurgical instruments have been coated with organic materials, such as polytetrafluoroethylene (“PTFE”) also known as TEFLON® or other polymers. Unfortunately, these low melting, volatile materials cannot withstand the high localized temperatures of the electric discharge between the electrode surface and the tissue. The resulting products of these melted, and at times, vaporized, coatings, are known to form harmful chemicals and undesirable products which deposit into the wound in the tissue being cut and cauterized. Surgical staffs have reported that after exposure to these vaporized organic coatings, flu-like symptoms result. This problem has been termed “polymer fume fever” or “TEFLON flu.” PTFE material is not always easy to apply and is not a good conductor. A further disadvantage is that a coating of organic material is melted in the very early stages of the electric discharge and therefore provides little or no improvement in the reduction of tissue adhesion. It is typical for the surface of a conventional stainless steel electrode to be roughened prior to conventional coating with PTFE material to improve the mechanical bond between the stainless steel and the coating. When the coating melts and reveals the roughened metal surface, this promotes increased pitting of the metal surface. This pitting can result in transfer of the metal from the electrode to the tissue. In addition the roughened metal surface can also exacerbate the problem of tissue buildup as discussed above.
Applying a layer of PTFE or TEFLON®, has another significant drawback, it has a tendency to scratch or abrade thereby diminishing the non-stick performance of the medical instrument. The non-stick properties of PTFE once diminished or lost, such as from being scratched or abraded, may not be readily repaired.
Another non-stick coating is discussed in U.S. Pat. No. 4,677,147. The coating involves the reaction of four components, i.e., thermostable polyorganosiloxane resin, a nonthermostable polyorganosiloxane resin, and two different metal salts of carbosylicacids. The need to use two different varieties of siloxane, and the metals, introduces cost and complexity. Silane coatings for glassware is described in U.S. Pat. No. 6,054,522.
Other examples are to plate the tip of the electrosurgical instrument with platinum or coat the tip with conductive ceramic. The plating or coating process can be quite complex and costly. Platinum is very costly, and ceramics can be quite brittle, the exposing the patient to risk of injury if pieces of ceramic chip or break off from the tip.
Another proposed solution to the problem of tissue adhesion is the use of a vibrating blade. (See, e.g., U.S. Pat. Nos. 4,674,498, 4,802,476, and 4,922,903.) These references describe electrosurgical apparatus including means for vibrating an electrosurgical blade during use to prevent buildup of tissue and debris on the blade. This technique requires the apparatus to include a means for vibrating and a means for coupling the vibrations to the electrosurgical instrument. This increases the cost and complexity of the apparatus and in some cases, for instance endoscopic surgery, may present great technological problems.
The issue of tissue buildup on electrosurgical instruments during electrosurgical procedures is a problem with these techniques that has yet to find an adequate solution. Although some solutions to this problem have been proposed, each has their own drawbacks. There is a long felt need for electrosurgical instruments to which tissue does not adhere, and which can be formed in a wide variety of shapes. It would be an improvement in the art to replace the current non-stick coatings with other anti-adhesion materials.